1. Field
The present invention relates to wireless communication and, more particularly, to a method and apparatus for transmitting data using multiple antennas and beamforming.
2. Discussion of the Background
In general, in a multi-cellular communication system, if communication between a base station and user equipment is performed in the state in which a frequency reuse factor ‘1’ is maintained in the same time and frequency band in each cell by not taking other cells into consideration, the performance of user equipment closer to a cell edge is greatly deteriorated owing to the distortion of a reception signal resulting from a reduction in the power of the reception signal and interference from other cells.
Some schemes have been researched so far in order to overcome a phenomenon in which performance is deteriorated due to this power reduction and interference. As one of the schemes, a cooperative transmission and reception scheme between multiple cells or between multiple transmission terminals is being discussed. The cooperative transmission and reception scheme is also called a Coordinated Multiple Point (CoMP) transmission and reception scheme in the LTE-A (Long Term Evolution-Advanced) standard. The CoMP transmission and reception scheme generally designates a method in which different base stations or multiple transmission terminals perform communication with the same user equipment through cooperation. That is, the CoMP transmission and reception scheme is a scheme in which a plurality of base stations performs downlink transmission or uplink reception through cooperation, and this scheme includes that a plurality of base stations performs downlink or uplink scheduling through cooperation. This scheme can improve a transmission power gain and signal sensitivity for pieces of user equipment having the intensity of a signal weaker than that of user equipment that is placed at the central area of a cell or an area having good signal reception sensitivity in a boundary area between cells or an area in which signal reception sensitivity is poor and can improve the transfer rate of the entire system by effectively removing the influence of interference.
Multiple antenna technology is technology for increasing a capacity or improving performance by using multiple antennas in the transmitter or receiver of a wireless communication system. Multiple antenna technology is technology for completing one entire message by gathering data fragments received from multiple antennas without depending on a single antenna path in order to receive one entire message. If the number of transmission antennas and the number of reception antennas are increased at the same time, frequency efficiency can be improved because a theoretical channel transmission capacity is increased in proportion to the number of antenna.
If the multiple antenna technology and the cooperative transmission and reception scheme are grafted, the intensity of a signal received by user equipment placed at a cell edge or user equipment placed in an area where reception sensitivity is poor can be increased. This method, however, can give interference to user equipment placed in another cell. If the number of transmission antennas is increased in order to remove this interference, there is a problem in that a power loss is generated because a beam width (beam width) is narrowed.